Continuous casting machine



United States Patent [72] Inventors Herbert Lemper; 2,709,842 6/1955Findlay 164/260 Thomas E. Rodwiclr; Paul M. Lowy, 2,815,551 12/1957llessenberg et a1... 164/260X Pittsburgh, Pennsylvania 3,088,181 5/1963Littlewood et al. l64/26l [21] Appl. No. 620,779 3,154,815 11/1964 Bieri164/261X [22] Filed March 6, 1967 3,258,815 7/1966 Reinfeld et a1.164/83X [45] Patented Nov. 24, 1970 3,293,707 12/1966 Olsson 164/83 [731 Ass'gnee Mesh g g g l Primary ExaminerJ. Spencer Overholser a Como" 8Assistant ExaminerR. Spencer Annear A tt0rney- Buell, Blenko 84Ziesenheim [54] CONTINUOUS CASTING MACHINE 9 Claims, 5 Drawing Figs.

US. Cl. "I... "in. Counterbalancing means for a vertically oscilla.164/83' 164,260. 164,282 tory mold structure used in a continuouscasting machine. The [S l] ht. Cl. B22d 17/32, impracticalmantel-weights or springs used in conventional 322d practices areeliminated by forming the mold structure as a [50] Field of Search164/82, 89, recipmcambk phmger in a suitably shaped cylinder surround260,261 4,4382 ing the mold structure. The plunger is supported withinthe cylinder by means of compressed fluid introduced therein [56] Rehnnmand under sufficient pressure to counterbalance the weight of the UNITEDSTATES PATENTS mold structure. A compressor or other source ofcompressed 3,047,915 8/1962 Barnard et a]. 164/154 fluid is coupled tothe cylinder, together with an accumulator 3,344,841 10/1967 Rys;164/154X to maintain the compressed fluid within the cylinder at a sub-3,358,743 12/ 1967 Adams 164/273X stantially constant pressureirrespective of the position of the 1,385,595 7/1921 Van Ranst 164/83mold structure along its reciprocatory path.

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INVENTORY M z M W w 4% Z P V. B

THEIR H I FOAM FY15 speed control and matching.

The mold-oscillating mechanism also includes an irreversible gear unitso-t'hat the oscillatory'load of the rather heavy mold structure cannotbe translated back as negative torque to the oscillator drive.

The present invention relates to'machines for the continuous casting ofsteel or'other metallic material and more'particularly to moldoscillating mechanisms and drive control means incorporated in suchmachines.

Although the'invention is described herein with reference tosteel-fabricatingequipment, it-will be appreciated that the invention isof general utility in other continuous casting procedures. i

it has long been known that the'highest casting speeds and bestsurfacequality of a continuous casting can be attained by oscillatingthe mold of the continuous casting machine. Usually the mold is moveddownwardly, or in'the direction of travel of the continuously cast slabor billet at a speed ranging from 100 percent to about 105 percent ofthe speed'of the casting. The mold structure is then returned'upwardlyor in mechanism and connecting linkages. This inv turn causes highlyundesirable fluctuations in motor speed, which impair the surfacequality of the casting. The speed regulator usually coupled tothe drivemeans is unable to cope with these speed I fluctuations because of theirhigh repetition rate and time delays inherent in the drive means.

More specifically, conventional mold oscillator drive means aredeficient in at least three respects, which'aggravate the problem ofspeed fluctuations, and proper control of themold oscillations. One ofthe principle causes of motor speed fluctuations is the overhaulingtorque on the cam during the quick return or upstroke'of the moldstructure. Although the weight of the mold structure is usuallycounterbalanced in some fashion, the totalrnass of the mold structureplus the counterweight is considerably increased, and the inertialforces thereof increase the overhauling or negative'torque at the drivemeans through the cam and gear' reduction unit usually associatedtherewith. It is one of the features of our invention, therefore, toisolate the drive means output from the overhauling torques applied tothe cam through'the provision of a selflocking or irreversible speedreduction unit. Thus, the torques applied to the output shaft of thereduction unit cannot be transmitted therethrough to-the drivemeanscoupled to the input shaft of the unit. As a result whenoverhauling or negative torque forces are transmitted back to the camshaft, the latter can only speed up to an extent which matches the noload speed of the drive means.

In continuous casting machines wherein the mold structure is oscillatedvertically, various forms of counterbalancing means have been used in anattempt'to achieve substantial reduction in drive requirements. Inaccordance with known practices, counterweights and springs have beenvariously used. Counterweights have proven to be impractical because thecorresponding increase in total mass increases the positive and negativeacceleration forces requiredto overcome the inertia of the structureplus the counterweight. This problem is seriously aggravated at the highcasting speeds of present day machines. Moreover, the use ofcounterweights considerably increase the overhauling torque mentionedpreviously.

Attempts have been made to overcome the disadvantages of counterweightsthrough the use of counterbalancing springs. Owing to floor spacelimitations, however, a counterbalancing spring with a high spring ratemust be used. This type of spring in turn produces large reactionalforces at the extreme deflections of the spring, which forces likewiseresult in high cam loadings and large drive requirements.

To overcome these deficiencies of the prior art, we provide a compressedair or other compressed fluid counterbalancing means. The moldstructure, in accordance with our invention, is arranged as areciprocating plunger in a suitably shaped cylinder surrounding the moldstructure. Desirably, accumulator means are associated with thecompressed fluid system to maintain substantially constant the availablebalancing forces at maximum plunger or mold structure displacements. Thefluid-operated cylinder offers a further advantage in that it cushionsthe abrupt changes in inertial forces caused by corresponding by abruptchanges in cam shape. A further advantage is the facile adjustment ofcounterbalancing force through a simple adjustment of fluid pressure inthe accumulator means.

Another problem encountered in the operation of conventional continuouscasting machines is the undesirable transfer of the aforementioned loadand drive fluctuations from the mold oscillator mechanism to thestraightener mechanism forming part of a continuous casting machine.This problem results from the mechanical coupling which hitherto hasbeen used between the oscillator and straightener drives. Suchmechanical coupling has been necessary in order to maintain the requiredspeed relation between the oscillational speed of the mold structure andthe speed of the straightener mechanism, during the forward or downwardportions of the mold oscillation cycle. In order that the speedrelationship be made adjustable to accommodate changing castingconditions a variable type of mechanical drive has been required.However, variable speed drives are undesirable because of their highmaintenance costs and lack of repeatability.

. Therefore, in accordance with another feature of our invention we haveovercome the last-mentioned problems by providing a speed-matchingcontrol system which permits the use of separately driven drivemechanisms for the oscillator and the straightener components of thecontinuous casting machine. As a result the disadvantages ofconventional mechanical couplings are eliminated, and the desired speedrelationship or matching is maintained between separate oscillator andstraightener drives by a suitable and novel speed control and matchingcircuitry.

In one arrangement of our control circuit a highly accurate speedregulator of conventional design is coupled to each of the moldoscillator and straightener drive means. Each of the speed regulators iscoupled in feedback relation to a tachometer in turn coupled to theassociated drive means. The

reference drive speed for the straightener regulator is provided by asignal derivedfrom the line speed of the casting. On the other hand, thespeed reference for the oscillator regulator is obtained from thetachometer feedback of the straightener drive, with the result that themold oscillator drive follows precisely the straightener drive but isnotmechanically coupled thereto. Speed matching of the oscillator drivewith the straightener drive is made possible and adjustable by providinga potentiometer or other adjustable resistance means between thefeedback connection of the straightener regulator this purpose thepotentiometer desirably is provided with dial means for recordingsettings corresponding respectively to differing casting conditions.

Other objects, features, and advantages of the invention will becomeapparent as the following description of certain presently preferredembodiments thereof and presently preferred methods of practicing thesame proceeds.

In the accompanying drawings we have shown certain presently preferredembodiments of the invention and have illustrated certain presentlypreferred methods of practicing the same in which:

FIG. 1 is a schematic elevational view, partially sectioned, of one formof continuous casting machine arranged in accordance with the invention;

FIG. 1A is an enlarged, partial view of a portion of the mold oscillatordrive means shown in FIG. 1;

FIG. 1B is a cross-sectional view of the mold structure of thecontinuous casting machine illustrated in FIG. I and taken generallyalong reference line IB-IB thereof;

FIG. 2 is a sectional view of the drive means shown in FIG. 1A and takenalong reference line II-II thereof; and

FIG. 3 is a schematic circuit diagram of one form of speed control meansfor a continuous casting machine arranged in accordance with ourinvention.

Referring more particularly to the drawings and initially to FIG. 1, anexemplary continuous casting machine is arranged in accordance with ourinvention and includes in this example a vertically reciprocable moldstructure denoted generally by reference character and having agenerally vertically casting cavity 12 therein. The cavity 12, togetherwith the verticalto-horizontal guide roll structure 14 are arrangedalong a radius of curvature to which the casting 16 is conformed, as inconventional practices, in moving from the vertically casting moldstructure 10 to the horizontal straightening mechanism identifiedgenerally by reference character 18.

For maintenance of equipment and for starting the casting 16 a portionof the guide roll structure 14 is pivotally mounted for movement to thechain outline position 20 thereof. When initiating the casting aflexible dummy bar (not shown) or the like can be secured to theinitially formed end portion of the casting adjacent the lower moldaperture 22 in order to thread the casting through the roll guides 14,the straightener mechanism 18 and the remaining components of thecasting machine (not shown). A suitable dummy bar for this purpose isdescribed and claimed in a copending, coassigned application of HerbertLemper entitled FLEXIBLE DUMMY BAR filed Sept. 9, I966, U.S. Pat. Ser.No. 578,313, now U.S. Pat. No. 3,442,322. I

In the straightener mechanism 18 the casting 16 engages guide rollers 24and thereafter in succession a series of straightener roll stands 26.

In this arrangement of the invention, molten steel is supplied to themold structure 10 from tundish 28, which may concurrently serve aplurality of similar mold structures associated with other strands (notshown) of the casting machine.

In order to maintain the highest practical casting speeds and theoptimum surface quality of the casting, as aforesaid, it is necessary tooscillate vertically the mold structure 10. This is accomplished by anoscillator drive including reduction unit 30 and an electric motor drive32. As better shown in FIGS. 1A and 2, the reduction unit 30 includesspur gear 34 and worm gear 36 mounted on shaft 38 for rotation therewithby worm 40 mounted on the output shaft of the drive motor 32 andenmeshed with the worm gear 36. In this example the worm 40 forms partof a gear assembly having a ratio such that an overhauling torqueapplied to the reduction unit 30 cannot reverse the worm 40 so as tocouple the overhauling torque to the motor electric drive 42.

The spur gear 34 is enmeshed with a related spur gear 42 mounted onshaft 44 together with cam 46 for rotation therewith. Likewise mountedon the reduction unit 30 is a pivoted cam follower 48 having a followerwheel 50 disposed in engagement with the cam periphery. The follower 48is pivoted to the casing of the reduction unit 30 as denoted byreference character 52 and an operating link 54 in turn is pivotallyconnected to the cam follower 48 and to an oscillating lever 56. Thelever 56 is pivoted at its fulcrum 58 to the adjacent supportingframework of the continuous casting machine, and the other end of thelever 56 is pivotally coupled to the vertically movable portion 60 ofthe mold structure 10. Accordingly, oscillating movements of theconnecting link 54 by the cam follower 48 are translated intocorrespondingly opposite oscillating movements of the mold plunger 60.In this arrangement the cam 48 is of dual surface configuration. Whenthe cam is rotated in the direction denoted by arrow 62 the curvedportions 64 of its periphery permit the mold plunger 60 to descend at arelatively slower speed consistent with the lineal speed of the castingwhile the relatively steep portions 66 of the cam 46 raise the moldplunger 60 at a faster rate. Accordingly, two oscillation cycles areimparted, in this example, to the mold plunger 60 for each rotation ofthe cam 46. The amplitude of the oscillation is dependent upon theparticular pivot aperture 68 at which the connecting link 54 is pivoted.

As pointed out previously, it is highly desirable to provide a suitablecounterbalancing means for the oscillating portion of the mold structure10 without introducing additional mass or reactive forces. Referringagain to FIG. 1 of the drawings one form of counterbalancing means isillustrated therein and arrangedin accordance with our invention. Thus,the aforementioned mold plunger 60 having the mold cavity 12 is coupledin this example to the other end of the lever 56 by a second connectinglink 70. The link 70 is pivotally connected at its upper end, as denotedby reference character 72, to the plunger 60 and at its lower end to thelever 56.

The mold plunger 60 is mounted for reciprocation within cylinder 74. Asbetter shown in FIG. 1B the plunger 60 is of stepped, generallycylindrical configuration and thus is provided with circumferentiallyextending shoulder 76. The inner wall surface of the cylinder 74 is ofcomplementary configuration, and the inner periphery thereof is steppedto form an inwardly disposed circumferentially extending shoulder 78.The necked down portion of the mold plunger 60 is sealed to theconstricted or shouldered portion 78 of the cylinder in this example bya pair of O-rings or the like 82. In a similar manner the thickenedportion 84 of the mold plunger 60 is sealed to the upper end portion ofthe cylindrical wall by similar sealing means such as O-rings 86.

As better shown in FIG. 1 of the drawings, the mold plunger 60 isillustrated in its uppermost position, as indicated by the solidoutlines thereof. The lowermost position of the plunger 60 is denoted byits dashed outline 88. Therefore, during the entire reciprocatory cycleof the mold structure 60 an annular space of varying length remainsbetween the plunger shoulder 76 and the cylinder shoulder 78 of the moldstructure. A suitable pressurized fluid such as compressed air isintroduced into the space 90 to serve as a fluid cushion, which in thisexample, is maintained under sufficient pressure to counterbalance theentire weight of the plunger 60. The weight of the plunger 60 is thuscounterbalanced without increasing the mass which must be moved by theoscillator drive 32. The inertia of the counterbalanced mold plunger 60remains the same in contradistinction to the conventional practice ofusing counterweights. Likewise the use of pressurized fluidcounterbalancing means does not involve the application of reactiveforces to the oscillator drive 32 as occasioned by the use ofconventional spring-counterbalancing means.

Pressurized fluid is supplied to the space 90 by means of an inletconduit 92 coupled to the cylinder 74 through which compressed fluid issupplied by a suitable pump denoted by reference character 94. Desirablyan accumulator tank 96 is coupled in the inlet conduit 92 between thepump 94 and the cylinder 74. The tank 96 preferably is of sufficientvolume that the contraction and expansion of the space 90 duringreciprocation of the mold plunger 60 will not significantly increase ordecrease the pressure of the fluid within the compressed fluid systemincluding, .of course, the space 90. Duringreciprocation of the moldplunger, pressurized fluid will be caused to flow to and from theaccumulator tank 96 as indicated by doubleheaded arrow 98.

Desirably a suitablepressure control means 100 is mounted in theaccumulator tank 96, in order to control an on/off switch 102 in thepower leads 104 of the pump 94 in the conventional manner. Thus when thepump 94 is energized pressurized fluid is transmitted to the accumulatortank 96 through the inlet conduit 92' as denoted by arrow 106. Thepressure control 100 can of course be adjusted .to a fairly small cyclicpressure variation in accordance with known practices, in order tomaintain the fluid pressure in the counterbalancing space 90substantially constant.

As denoted previously, from the mold structure the continuous casting 16is conducted along an 'arcuate path whereby the casting is' turned fromits vertical casting direction to a horizontal disposition for furtherfabrication. Therefore, the casti'ng16 must be straightened as notedprevi ously in the straightener 18. Also, it is essential that the speedof the plunger 60 during the downward component of its oscillation cyclebe exactly matched in accordance with a predetermined speed ratio, withthe speed of the straightener rolls 108. It is also essential that theaforementioned speed ratio can be reproducibly adjusted in order toadapt the continuous casting machine to different casting conditions. Asnoted above it has not-beenpossible with conventional apparatus tomaintain a predetermined speed matching with a high degree of accuracy.Moreover, it was not possible to vary the speed ratio between thestraightener rolls 108 and the down component of the mold oscillationcycle in a reliably reproducible manner.

Accordingly, as better shown in FIG. 3 we have provided the straightenerroll drive 26 witha conventional high accuracy-speed regulator 28 havingtachometer feedback 112. A reference signal is supplied to thestraightener speed regulator 110 through conductor 114. The conductor114 is connected to suitable and conventional mechanism 115 forindicating the speed of the casting 16 in the form of arelatedelectrical signal. The tachometer 112 output is one of thestraightener drive motors 26 is fed back in the usual fashion to theassociated speed regulator 110 through conductor 116 but is alsoconducted to a conventional, high accuracy speed regulator 118 for themold oscillator drive motor 32. The signal from the tachometer 112 thusforms the speed reference signal on input conductor 120 for thelast-mentioned of oscillator speed regulator 118. A conventionaltachometer 122 is also coupled to the oscillator drive motor 32 and itsoutput is fed back through conductor 124 to the oscillator speedregulator 118.

With this arrangement, the speed of the oscillator drive motor 32 can bematched exactly, according-to the desired speed ratio, withthespeed ofthe work roll drive 26 since the oscillator speed regulator 118 iscontrolled by the speed of the straightener drive motor 26'. As thestraightener speed regulator 110 is controlled bythe line speed, thecircuit arrangement of FIG. 3 thus preserves the predetermined desiredspeed relationship between the straightener drive, motors 26 andthe.

oscillator drive motor 32. For example, theoscillator drive can beclosely controlled to maintain the speed of the down component of themold plunger 60 exactly at a'given percentage of the lineal castingspeed, which relationship in turn is related to line speed.

-In order to provide means for varying the speed matching or speed ratiobetween the straightener drive motors 26 on the one hand and theoscillator drive on the other, reproducible speed ratio-adjusting meansare providedby the invention, and can be calibratedto differing speedratios if desired. One form of such ratio-adjusting means includespotentiometer 126 coupled in speed reference conductor 120 of theoscillator speed regulator 118. The potentiometer 126 is capable ofadjusting the ratio. of tachometer 112 output to the oscillator speedregulator 118 in relation to the tachometer 112 feedback to thestraightener speed regulator 110. Thus'a given potentiometer settingalways produces a given speed ratio between the straightener drivemotors 26 and the oscillator drive motor 32.

In view of the foregoing it will be evident that novel and efficientforms of continuous casting machines have been disclosed herein. Thevarious features of the invention cooperate to produce a controllableand uniform speed of casting, which is reproducibly variable to meetdifferent casting conditions.

While we have shown and described certain presently preferredembodiments of the invention and have illustrated presently preferredmethods of practicing the same,-it is to be distinctly understood thatthe invention is not limited thereto but may be otherwise variouslyembodied and practiced within the scopeof the following claims.

We claim:

1. A continuous casting machine comprising a mold structure open atopposite ends, means for mounting said mold structure for reciprocationand for reciprocating the mold structure in the direction of saidcasting, and separate counterbalancing means coupled to said moldstructure for applying a fluid pressure thereto for supporting at leastpart of the weight of said mold structure, said counterbalancing meansbeing disposed for least partially removing the load of said moldstructure from said reciprocating means.

2. In a continuous casting machine having an oscillatable mold structureand a straightener mechanism for straightening a casting issuing fromsaid mold structure, said mold structure and said straightener mechanismbeing positioned in tandem along a path of said casting, the combinationcomprising oscillator drive means for said mold structure, straightenerdrive means for said straightener mechanism, a speed regulator andtachometer coupled to each of said drive means, circuit means forcoupling each of said tachometers in feedback relation to the speedregulator of the associated drive means and for coupling an output ofthe tachometer of one of said drive means to the reference input of thespeed regulator of the a other drive means, and additional circuit means.for coupling the reference input of the other of said speed regulatorsto casting speed-sensing means.

3.'The combination according to claim 2 wherein variable resistancemeans are coupled between said reference input of said other drive meansspeed regulator and said tachometer output of said one drive means forvarying the matched speed ratio between said drive means.

4. The combination according to claim 1 wherein said mold structureincludes a mold plunger mounted for reciprocation in an outer shellclosely surrounding the plunger, said shell and said plunger havingspaced juxtaposed projections formed thereon respectively and defining afluid cushion spaced therebetween and within said shell.

- Y 5. The combination according to claim 1 wherein said continuouscasting machine includes a straightening mechanism for straightening acasting issuing from said mold structure,

drive means for said straightening mechanism, said mold structure andsaid straightening mechanism being positioned in tandem along a path'ofsaid casting, and circuit means are coupled between said oscillatingmeans and said straightening drive means for maintaining a predeterminedspeed ratio therebetween.

6. The combination according to claim 4 wherein a fluid inlet conduit iscoupled to said shell in communication with said cushioning space, andcompressor and accumulator means are coupled to said inlet conduit.

7. The combination according to claim 4 wherein said mold plunger andsaid shellare of complementary stopped outer and innerconfigurationsrespectively, the stepped portions of said plunger beingsealed respectively to the stepped portions of said shell to enclosedsaid fluid cushion space.

8. The combination according to claim 1 wherein said reciprocating meansinclude a drive motor and gear reduction unit, said unit comprising anirreversible worm coupled to the output shaft of said drive motor.

tachometers in feedback relation to the associated speed regulator, saidcircuit means in addition coupling an output of one of said tachometersto a reference input of the speed regulator associated with the other ofsaid tachometers, and additional circuit means for coupling thereference input of the other of said speed regulators to casting speedsensing means.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 542,117 Dated November 24 1970 Inventor) Herbert Lemper et a1 It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 3, line 51 "rollers" should read rolls Column 5, line 42, "is"should Signed and sealed this 4th day of May 1971 (SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E SCHUYLER, J' Attesting OfficerCommissioner of Patent ran I-IA Ann [in read of line 48 "of should reador line 68 after "drive" insert moto' 32 Column 7 line 6 after"positioned" cancel the peri'

